[Uterine activity under tocolysis through a beta-sympathomimetic (author's transl)].

The actual mechanism of tocolytic effect of beta-mimetics is not yet known. While they are able to stop labour, the effect in vitro on myometral filaments is very different. In contrast to this, the socalled Ca++ -antagonists have an excellent relaxing effect on myometrium in vitro, but they are clinically ineffective. To clear up the mechanism of tocolysis, the uterine activity under tocolytic therapy was observed by external tocography. Whereas in normal pregnancy the portion of Braxton-Hicks-contractions and phases of inactivity--equivalent to the intervals of labour -- increases and the portion of Alvarez waves decreases, under tocolysis these changes are not to be found for a long time. The portion of Braxton-Hicks-contractions and phases of inactivity together is smaller than in normal pregnancy. The proportion of Braxton-Hicks-contractions to phases of inactivity corresponds well to normal pregnancy. The changes of uterine activity in normal pregnancy are explained as a process of increasing coordination. The tocolytic effect is regarded as a disturbance of this process.